Transcript No Slide Title

Food preservation
Introduction
 main methods are:
 drying
 curing (smoke or salt)
 canning & bottling
 pickling
 freezing
 nutritional value is usually decreased - & also flavour,
colour, aroma
 use best available produce for preservation not the worst
see http://www.vita.org/pubs/docs/udc1.html and
http://www.vita.org/pubs/docs/udc2.html also
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http://www.unu.edu/unupress/unupbooks/80478e/80478E00.htm#Contents
Canning / bottling
 heat to sterilise and exclude air
 sterilising by:
 water bath
 pressure cooker - for low acid foods achieves higher Ts
 canning is most expensive method of preservation after
freezing - energy requirements
 best method for long duration storage
 home canning may be less expensive than buying
commercially canned produce
 water baths and pressure canners available commercially
 cost of labour should be included in analyses
 co-operatives?
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Freezing
 fruit not usually blanched or cooked before freezing
 vegetables are blanched
 freeze before packing together to prevent sticking
 storage life of a year - write date
 Asian Inst. of Tech. in Thailand have developed freezing
unit that runs on solar energy
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Drying
 when 80 to 90% of water removed, cannot support
microbial life
 also salts, sugar, proteins increase their concentration & also inhibit microbial reproduction
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 3 methods:
 sun drying - no pre-treatment - dried in the open long time- may become contaminated - sun-drying
destroys some vitamins but weight for weight dried
fruit is more nutritious than fresh
 solar drying - dried in trays covered with glass or
plastic - needs intense cloudless sunlight & dry air 1 to 3 days
 convection drying - 30° to 60°C optimum - fruit & veg
retain more of vitamins - high cost of energy a problem
sun / solar drying the least expensive preservation
methods
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 improved drying of ingredients for preparation of
Nepalese Gundruk - made from mustard, radish and
cauliflower (!) make reduces loss of carotenoids & makes
more nutritious
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Curing
 methods :  salt (dry or as brine)
 vinegar
 oils
 possibly combined with smoking to retard or prevent
growth of micro-organisms
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Salting
 cured food - especially salted or brined food can store
longer than dried food - vegetables, fish, cheese
 if sufficient moisture as in vegetables - can be dry salted
- otherwise use brine
 draws out water and in high concentrations, inhibits
micro-organisms; in smaller concentrations, salt promotes
lactic acid producing bacteria - acidity eventually
exceeds tolerance of bacteria including the lactic acid
producers
Fermenting before salting
• cabbage may be fermented - sauerkraut - before salting
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Pickling
 pickling - uses vinegar & spices instead of, or in addition
to salt - e.g. fruit (mango pickle), onions, fish
Smoking
 smoking - mostly meat and fish - but sometimes
vegetables
 tie to string and hang over an open fire or use a specially
constructed smoke box - biltong
 some vegetables are salted, oiled, spiced before smoking
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Parboiling

means to partly cook by boiling or steaming

mainly rice; in India > 50% of paddy is parboiled soaking, steaming, then drying
 modern Indian method utilises hot water for soaking at
70 to 80° C for 3.5 hours and eliminates the steaming
process
 main object of parboiling is to harden the grain and reduce
milling losses
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 parboiling also minimises losses during milling of thiamine,
riboflavin, and niacin in rice grain -
 during the parboiling process, water-soluble nutrients are
driven from the outer layers into the inner layers of the
grain and thus escape removal during milling
 some sorghum varieties are soft, and respond well to
parboiling for subsequent preparation of semolina
 bulgur wheat represents a successful parboiling variety
parboiling achieves case-hardening so is excellent method
of treatment prior to storage (as well as prior to milling)
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Pasteurisation
Mainly for milk but pasteurisation helps shelf life of
other foods, e.g. of Kanji in N. India - made from carrots,
salt, mustard seed & hot chilli
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Milling - flour
 flour can be made from any cereal and many root crops
 in addition to milling to make flour, milling can also mean
the removal of the coarse fibrous bran or the seed coat especially rice - loses nutrient value (unless parboiled)
though iron availability improves
 roller mills most common
 mix wheat flour with QPM (Quality Protein Maize) for
compound
 semolina is the left over hard bits - used directly or
for pasta
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Baking - cakes and bread
 mainly for town areas but village bakeries possible
 new approaches needed, e.g.:
 in Jamaica, "Bammy bread" - round cakes soaked in
coconut milk and grilled now being packaged, frozen
and exported to Europe and North America
 cassava cheese bread in Brazil
Pasta & noodles
Made from wheat flour - good way of preserving wheat easy to cook - used as staple in Italy - potential for other
wheat growing areas such as India but people need to
become familiar - needs marketing, etc.
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Chips and crisps
 produced in many countries including India, Kenya, etc
 mainly made and consumed in urban areas
 high income for farmers growing the special varieties
needed
 in Colombia, improved technologies for producing
cassava chips have been promoted to supply the
expanding market for animal feed concentrates
Heat and serve preparation
 increasing trend - some being developed are based on
cassava - but needs quite sophisticated equipment
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Vegetable oil extraction
 Africa imports large amounts of vegetable oil for cooking
even though there is an immense capacity for local
production
 many designs exist, see e.g.
http://www.attra.org/attra-pub/oilseed.html
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 traditional Indian method = the ghani - now widespread
elsewhere :  wooden mortar and pestle;
 mortar is fixed to the ground, and the pestle
located in mortar,
 raw material crushed by friction and pressure
 an animal is required to move the pestle
 oil pressed out & runs through hole at the bottom
of the mortar
 residue (cake) scooped out
 two animals are required, since any one animal
tires after 3-4 hours
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 improved technologies for extracting oil include:
 motorised ghanis
 oil presses
 oil expellers
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 most oil presses work on a similar principle:
 raw materials are placed in heavy perforated or slotted
metal cage and a metal plunger is used to press out the
oil
 main differences in design are:
 method used to move the plunger.
 amount of pressure in the press
 size of the cage
 plunger can be moved either manually or with the
aid of a motor
 screw-thread or a hydraulic system
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 oil presses can be manufactured locally:
 for a screw-press, however, a lathe is needed to
manufacture the screw
 hydraulic presses may be manufactured locally if
lorry jacks are available
 important that mineral oil used with either screw
or hydraulic press does not contaminate the vegetable
oil
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
oil expellers - continual operation:
 use a horizontally-rotating screw which feeds
oil-bearing raw material into barrel-shaped outer
casing with perforated walls
 raw material is continuously fed to the expeller,
which grinds, crushes, and presses out the oil as it
passes through the machine
 oil flows through the perforations in the casing and
is collected underneath
 residue, or oilcake, is pushed out of the end of the
unit
 most small expellers are power-driven
 due to the wear and tear, screw needs to be repaired
/ replaced frequently - need skills and resources for
maintenance to be available locally
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
clarification:
 crude oil contains a suspension of fine pulp and fibre
from plant material,
 also contains smaller quantities of water, resins,
colours, and bacteria which makes it dark in colour,
 contaminants removed by clarifying the oil, either by
allowing the oil to stand undisturbed for a few days
& then removing the upper layer, or by using a clarifier
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 if further clarification needed, oil may be filtered
through a plastic funnel which has been fitted with a
fine filter cloth,
 oil is then heated to boil off traces of water and
destroy any bacteria,
 for raw materials which are processed wet (such as
coconut), heating is applied prior to clarification in
order to break the emulsion
 when these impurities are removed, the shelf-life
of the oil is extended from a few days to several
months, provided stored properly
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Germination and malting
 soaking in water overnight followed by germination or
sprouting of the grain very common household practice,
especially for pulses
 several enzyme systems become active and bring about
changes in the nutritive value of pulses: vitamin C,
increases in significant amounts after germination as
does folic acid in chick-pea and ragi
 anti-nutritional factors such as phytate, trypsin
inhibitor, and haemaglutinins are broken down on
germination

pronounced reduction of phytate - organic acid which
can lead to mineral deficiency - in both ragi (finger
millet) and bajra (pearl millet)
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 malting: grain spread in a thin layer and steeped in water
so that it can germinate - germinated grain, which forms
inside the husk, is called malt - dried and then cracked,
liberating the malt from the husk
 malted grain useful in making enzyme-rich flour as well
as brewing
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Fermentation
(see http://www.fao.org/docrep/x2184E/x2184e09.htm)
 submerged fermentation - raw material submerged in
water within a bioreactor or fermenting vat
 solid substrate fermentation - food spread out over trays
or leaves - uses less water
 fermentation starters (prepared from the growth of
moulds) on raw or cooked cereals is more commonly
practised than using malted cereals
 improved starter culture (e.g.) needed to accelerate
speed of fermentation & to produce uniform end product
in which losses of vitamins & other micronutrients
minimised
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 olive sediment, from traditional olive oil extraction
mills was useless - now fermented product sufficiently
digestible for use as animal feed
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Wine-making
 use of variety of fruit growing - buy when price low - for
local consumption among neighbours or with better
quality control - bottling and sale in local shops
 fruit wines such as papaya and banana wine now
produced and sold commercially
Fruit juice
 see notes on processing of citrus juice
 expansion of Baobab fruit juice extract in Malawi refreshing said to be a cure for hangovers - roadside
extraction - keeps for 6 months - no special treatment
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Starch extraction
 from most cereals and many root crops
 widely used in producing glucose syrup, adhesives, paper,
textiles, beer, pharmaceuticals, food, household textiles
such as carpets, and rubber latex
 potential for export
 canna in Vietnam and sweet potatoes in China used as
source of starch for transparent noodles (traditionally
made from mungbean starch) - luxury food across Asia
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 can be produced at village level - starch removed from
plant by kneading with the hands or trampling by feet or,
in more highly mechanised operations, by a spray of water;
starch-laden water runs into a settling container
 resulting starch "milk" contains starch in suspension and
soluble solids in solution
 starch is separated and washed free from the solubles,
the water is removed (industrially by centrifugal action
or in local methods it overflows - potential for water
pollution a problem
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Jam and pectin production
 jam making not very common in rural areas of DCs because
of large amounts of sugar - but popular in towns and cities
- mainly made by medium sized operations
 pectin extracted from fruit for use in jam-making and
in jellies and other foods
 many DCs import pectins even though great variety of
natural perishable products that contain pectins,
especially fruits
 wasted in great quantities - extractable from fruit
“waste”
 extraction depends on pH, temperature and heating
times and the quality of the fruits
 pectin now also made from cocoa waste
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Animal feed
Increasing potential as more livestock produced intensively,
good income if near market - examples:
 can use by-products from oil extraction such as
groundnuts, sunflower
 dried cassava chips
 sliced fresh husks from cocoa used as a substitute
for wheat bran to feed to pigs and rabbits.
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Papain from papaw
 latex obtained by making incisions on the surface of the
green fruits early in the morning and repeating every
4 or 5 days until the latex ceases to flow
 tool used has to be bone, glass, sharp-edged bamboo or
stainless steel (knife or razor blade)
 tappers hold coconut shell, clay cup, or glass, porcelain or
enamel pan beneath the fruit to catch the latex, or a
container like an "inverted umbrella" is clamped around
the stem - latex coagulates quickly and is spread on fabric
and oven-dried at a low temperature, then ground to
powder and packed in tins (sun-drying tends to discolour)
 tap 1,500 average-size fruits to harvest 1.5 lb papain
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 used:
 as meat tenderiser (now even prior to slaughtering)
 to clarify beer
 to treat wool and silk before dyeing
 to de-hair hides
 in rubber manufacture
 on tuna liver before extraction of the oil which is
thereby made richer in vitamins A and D
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 toothpastes, cosmetics and detergents, as well as
pharmaceutical preparations to aid digestion
 to treat ulcers
 dissolve membranes in diphtheria
 reduce swelling, fever and adhesions after surgery
 applied on meat impacted in the gullet
 injected in cases of slipped spinal discs or pinched
nerves
 NB - some individuals allergic to papain in any form and
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to meat tenderised with papain
Soap and beauty products
 potential for village based industry
 e.g. fat extracted from cocoa beans from diseased pods
or beans that have germinated during drying being used to
make soap and pomade (cold cream) in W Africa
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